Recently, we demonstrated for the first time in human system the coexistence of tumor specific cytotoxic and suppressor lymphocytes. We now propose to: (1) determine the clinical significance of cytotoxic and suppressor cells by a prospective study of patients' lymphocytes throughout their clinical course, (2) elucidate the mechanisms of interactions between cytotoxic and suppressor lymphocytes by determining the tumor specificity of suppression, the possible involvement of soluble-suppressive factor and the possible modulation of the interactions by thymic-hormonal factor and various drugs, (3) differentiate tumor-specific cytotoxicity from natural cytotoxicity by separating the effector cells responsible for these two types of cytotoxicity and the use of various drugs to eliminate natural cytotoxicity.